#include <stdio.h>

int main()
{
    int hour1;
    int hour2;
    int minute1;
    int minute2;
    int sum1;
    int sum2;
    scanf("%d %d",&sum1,&sum2);
    hour1 = sum1 / 100;
    hour2 = sum2 / 100;
    minute1 = sum1 % 100;
    minute2 = sum2 % 100;
    hour1 = hour2 - hour1;
    minute1 = minute2 - minute1;
    if(minute1 < 0){
        hour1 = hour1 - 1;
        minute1 = minute1 + 60;
    }
    printf("%02d:%02d\n",hour1,minute1);
    return 0;
}